<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
      var a = prompt('班长口袋里有多少钱？')  
      if (a >= 2000) {
          alert('请大家吃西餐')
      }else if (a >= 1500) {
          alert('请大家吃快餐')
      }else if (a >= 1000) {
          alert('请大家喝饮料')
      }else if (a >= 500) {
          alert('请大家吃棒棒糖')
      }else {
          alert('班长下次把钱带够')
      }
    </script>
</body>
</html>